Systems and methods for monitoring stimulation drift in an electrical stimulation system

ABSTRACT

A method for monitoring stimulation drift includes directing electrical stimulation through electrodes of a lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of an implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 63/315,852, filed Mar. 2, 2022, which is incorporated herein by reference.

FIELD

The present invention is directed to the area of implantable electrical stimulation systems and methods of making and using the systems. The present invention is also directed to systems and methods for monitoring stimulation drift in an electrical stimulation system and, in some embodiments, altering the stimulation in view of the stimulation drift.

BACKGROUND

Implantable electrical stimulation systems have proven therapeutic in a variety of diseases and disorders. For example, spinal cord stimulation systems have been used as a therapeutic modality for the treatment of chronic pain syndromes. Peripheral nerve stimulation has been used to treat chronic pain syndrome and incontinence, with a number of other applications under investigation. Deep brain stimulation can be used to treat a variety of diseases and disorders.

Stimulators have been developed to provide therapy for a variety of treatments. A stimulator can include a control module (with a pulse generator) and one or more stimulator electrodes. The one or more stimulator electrodes can be disposed along one or more leads, or along the control module, or both. The stimulator electrodes are in contact with or near the nerves, muscles, or other tissue to be stimulated. The pulse generator in the control module generates electrical pulses that are delivered by the electrodes to body tissue.

BRIEF SUMMARY

One aspect is an electrical stimulation system that includes a lead having electrodes disposed along a distal portion of the lead and an implantable control module coupled, or coupleable, to the lead and configured for implantation in a patient. The implantable control module including a processor configured for performing actions, including directing electrical stimulation through the electrodes of the lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of the implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position by altering at least one of i) the selection of the one or more electrodes or ii) the stimulation amplitude for at least one of the one or more selected electrodes and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.

Another aspect is a method for monitoring stimulation drift. The method includes directing electrical stimulation through electrodes of a lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of an implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position by altering at least one of i) the selection of the one or more electrodes or ii) the stimulation amplitude for at least one of the one or more selected electrodes and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.

A further aspect is a non-transitory computer-readable medium having processor-executable instructions for monitoring stimulation drift, the processor-executable instructions when installed onto a device enable the device to perform actions, the actions including: directing electrical stimulation through electrodes of a lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of an implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position by altering at least one of i) the selection of the one or more electrodes or ii) the stimulation amplitude for at least one of the one or more selected electrodes and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.

In at least some aspects, the modulating includes modulating the stimulation position during a plurality of modulation periods, wherein the modulation periods are separated by non-modulation intervals. In at least some aspects, the modulation period has a duration of at least 30 minutes and the non-modulation interval has a period of at least 30 minutes.

In at least some aspects, the modulating includes modulating the stimulation position continuously over the time period. In at least some aspects, the modulating includes modulating the stimulation position to provide stimulation positions during the modulation in at least three different quadrants around the primary stimulation position. In at least some aspects, altering the primary stimulation position includes altering the stimulation position only after confirmation from a user.

In at least some aspects, the modulating includes modulating the stimulation position; assessing whether a patient increases a stimulation intensity in response to the modulation; and when the assessment is negative, increasing a change in the stimulation position from the primary stimulation position. In at least some aspects, the performing includes performing the altering of the primary stimulation position, the actions including an automated closed loop adjustment of the primary stimulation position in response to stimulation drift.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified.

For a better understanding of the present invention, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, wherein:

FIG. 1 is a schematic view of one embodiment of an electrical stimulation system;

FIG. 2 is a schematic side view of one embodiment of an electrical stimulation lead;

FIG. 3 is a schematic overview of one embodiment of components of a stimulation system, including an electronic subassembly disposed within a control module;

FIG. 4 is a schematic side view of an embodiment with portions of three percutaneous leads disposed next to each other;

FIG. 5 is a schematic top view of a portion of one embodiment of a paddle lead;

FIG. 6 is a flowchart of one embodiment of a method for monitoring stimulation drift;

FIG. 7 is a graphical illustration of stimulation position with a center stimulation position; and

FIG. 8 is flowchart of one embodiment of a method for monitoring whether the modulation of the stimulation position produces noticeably different stimulation.

DETAILED DESCRIPTION

The present invention is directed to the area of implantable electrical stimulation systems and methods of making and using the systems. The present invention is also directed to systems and methods for monitoring stimulation drift in an electrical stimulation system and, in some embodiments, altering the stimulation in view of the stimulation drift.

Suitable implantable electrical stimulation systems include, but are not limited to, a least one lead with one or more electrodes disposed on a distal portion of the lead and one or more terminals disposed on one or more proximal portions of the lead. Leads include, for example, percutaneous leads, paddle leads, cuff leads, or any other arrangement of electrodes on a lead. Examples of electrical stimulation systems with leads are found in, for example, U.S. Pat. Nos. 6,181,969; 6,516,227; 6,609,029; 6,609,032; 6,741,892; 7,244,150; 7,450,997; 7,672,734; 7,761,165; 7,783,359; 7,792,590; 7,809,446; 7,949,395; 7,974,706; 8,175,710; 8,224,450; 8,271,094; 8,295,944; 8,364,278; 8,391,985; and 8,688,235; and U.S. Patent Application Publications Nos. 2007/0150036; 2009/0187222; 2009/0276021; 2010/0076535; 2010/0268298; 2011/0005069; 2011/0004267; 2011/0078900; 2011/0130817; 2011/0130818; 2011/0238129; 2011/0313500; 2012/0016378; 2012/0046710; 2012/0071949; 2012/0165911; 2012/0197375; 2012/0203316; 2012/0203320; 2012/0203321; 2012/0316615; 2013/0105071; and 2013/0197602, all of which are incorporated herein by reference. In the discussion below, a percutaneous lead will be exemplified, but it will be understood that the methods and systems described herein are also applicable to paddle leads and other leads.

A percutaneous lead for electrical stimulation (for example, deep brain, spinal cord, or peripheral nerve stimulation) includes stimulation electrodes that can be ring electrodes, segmented electrodes that extend only partially around the circumference of the lead, or any other type of electrode, or any combination thereof. The segmented electrodes can be provided in sets of electrodes, with each set having electrodes circumferentially distributed about the lead at a particular longitudinal position. A set of segmented electrodes can include any suitable number of electrodes including, for example, two, three, four, or more electrodes.

Turning to FIG. 1 , one embodiment of an electrical stimulation system 10 includes one or more stimulation leads 12 and an implantable pulse generator (IPG) 14. The system can also include one or more of an external remote control (RC) 16, a clinician's programmer (CP) 18, an external trial stimulator (ETS) 20, or an external charger 22. The IPG and ETS are examples of control modules for the electrical stimulation system.

The IPG 14 is physically connected, optionally via one or more lead extensions 24, to the stimulation lead(s) 12. Each lead carries multiple electrodes 26 arranged in an array. The IPG 14 includes pulse generation circuitry that delivers electrical stimulation energy in the form of, for example, a pulsed electrical waveform (i.e., a temporal series of electrical pulses) to the electrode array 26 in accordance with a set of stimulation parameters. The implantable pulse generator can be implanted into a patient's body, for example, below the patient's clavicle area or within the patient's buttocks or abdominal cavity or at any other suitable site. The implantable pulse generator can have multiple stimulation channels which may be independently programmable to control the magnitude of the current stimulus from each channel. In some embodiments, the implantable pulse generator can have any suitable number of stimulation channels including, but not limited to, 4, 6, 8, 12, 16, 32, or more stimulation channels. The implantable pulse generator can have one, two, three, four, or more connector ports, for receiving the terminals of the leads and/or lead extensions.

The ETS 20 may also be physically connected, optionally via the percutaneous lead extensions 28 and external cable 30, to the stimulation leads 12. The ETS 20, which may have similar pulse generation circuitry as the IPG 14, also delivers electrical stimulation energy in the form of, for example, a pulsed electrical waveform to the electrode array 26 in accordance with a set of stimulation parameters. One difference between the ETS 20 and the IPG 14 is that the ETS 20 is often a non-implantable device that is used on a trial basis after the neurostimulation leads 12 have been implanted and prior to implantation of the IPG 14, to test the responsiveness of the stimulation that is to be provided. Any functions described herein with respect to the IPG 14 can likewise be performed with respect to the ETS 20.

The RC 16 may be used to telemetrically communicate with or control the IPG 14 or ETS 20 via a uni- or bi-directional wireless communications link 32. Once the IPG 14 and neurostimulation leads 12 are implanted, the RC 16 may be used to telemetrically communicate with or control the IPG 14 via a uni- or bi-directional communications link 34. Such communication or control allows the IPG 14 to be turned on or off and to be programmed with different stimulation parameter sets. The IPG 14 may also be operated to modify the programmed stimulation parameters to actively control the characteristics of the electrical stimulation energy output by the IPG 14. The CP 18 allows a user, such as a clinician, the ability to program stimulation parameters for the IPG 14 and ETS 20 in the operating room and in follow-up sessions. Alternately, or additionally, stimulation parameters can be programed via wireless communications (e.g., Bluetooth) between the RC 16 (or external device such as a hand-held electronic device) and the IPG 14. In at least some embodiments, the RC 16 can be a mobile phone, tablet, desktop computer, or the like.

The CP 18 may perform this function by indirectly communicating with the IPG 14 or ETS 20, through the RC 16, via a wireless communications link 36. Alternatively, the CP 18 may directly communicate with the IPG 14 or ETS 20 via a wireless communications link (not shown). The stimulation parameters provided by the CP 18 are also used to program the RC 16, so that the stimulation parameters can be subsequently modified by operation of the RC 16 in a stand-alone mode (i.e., without the assistance of the CP 18).

For purposes of brevity, the details of the RC 16, CP 18, ETS 20, and external charger 22 will not be further described herein. Details of exemplary embodiments of these devices are disclosed in U.S. Pat. No. 6,895,280, which is incorporated herein by reference in its entirety. Other examples of electrical stimulation systems can be found at U.S. Pat. Nos. 6,181,969; 6,516,227; 6,609,029; 6,609,032; 6,741,892; 7,949,395; 7,244,150; 7,672,734; and 7,761,165; 7,974,706; 8,175,710; 8,224,450; and 8,364,278; and U.S. Patent Application Publication No. 2007/0150036, as well as the other references cited above, all of which are incorporated herein by reference in their entireties.

FIG. 2 illustrates one embodiment of a lead 112 with electrodes 126 disposed at least partially about a circumference of the lead 112 along a distal end portion of the lead 112 and terminals 135 disposed along a proximal end portion of the lead 112.

The lead 112 can be implanted near or within the desired portion of the body to be stimulated such as, for example, the brain, spinal cord, or other body organs or tissues.

Electrodes may be disposed on the circumference of the lead 112 to stimulate the target neurons or other tissue. Stimulation electrodes may be ring shaped so that current projects from each electrode radially from the position of the electrode along a length of the lead 112. In the embodiment of FIG. 2 , two of the electrodes 126 are ring electrodes 120. Ring electrodes typically do not enable stimulus current to be directed from only a limited angular range around a lead. Segmented electrodes 130, however, can be used to direct stimulus current to a selected angular range around a lead. When segmented electrodes are used in conjunction with an implantable pulse generator that delivers constant current stimulus, current steering can be achieved to deliver the stimulus more precisely to a position around an axis of a lead (i.e., radial positioning around the axis of a lead). To achieve current steering, segmented electrodes can be utilized in addition to, or as an alternative to, ring electrodes.

The lead 112 includes a lead body 110, terminals 135, at least one ring electrode 120, and at least one set of segmented electrodes 130 (or any other combination of electrodes). The lead body 110 can be formed of a biocompatible, non-conducting material such as, for example, a polymeric material. Suitable polymeric materials include, but are not limited to, silicone, polyurethane, polyurea, polyurethane-urea, polyethylene, or the like. Once implanted in the body, the lead 112 may be in contact with body tissue for extended periods of time. In at least some embodiments, the lead 112 has a cross-sectional diameter of no more than 1.5 mm and may be in the range of 0.5 to 1.5 mm. In at least some embodiments, the lead 112 has a length of at least 10 cm and the length of the lead 112 may be in the range of 10 to 70 cm.

The electrodes 126 can be made using a metal, alloy, conductive oxide, or any other suitable conductive biocompatible material. Examples of suitable materials include, but are not limited to, platinum, platinum iridium alloy, iridium, titanium, tungsten, palladium, palladium rhodium, or the like. Preferably, the electrodes 126 are made of a material that is biocompatible and does not substantially corrode under expected operating conditions in the operating environment for the expected duration of use.

Each of the electrodes 126 can either be used or unused (OFF). When an electrode is used, the electrode can be used as an anode or cathode and carry anodic or cathodic current. In some instances, an electrode might be an anode for a period of time and a cathode for a period of time.

Segmented electrodes may provide for superior current steering than ring electrodes because target structures are not typically symmetric about the axis of the distal electrode array. Instead, a target may be located on one side of a plane running through the axis of the lead. Through the use of a radially segmented electrode array (“RSEA”), current steering can be performed not only along a length of the lead but also around a circumference of the lead. This provides precise three-dimensional targeting and delivery of the current stimulus to neural target tissue, while potentially avoiding stimulation of other tissue. Examples of leads with segmented electrodes include U.S. Pat. Nos. 8,473,061; 8,571,665; 8,792,993; 9,248,272; 9,775,988; and 10,286,205; U.S. Patent Application Publications Nos. 2010/0268298; 2011/0005069; 2011/0130803; 2011/0130816; 2011/0130817; 2011/0130818; 2011/0078900; 2011/0238129; 2012/0016378; 2012/0046710; 2012/0071949; 2012/0165911; 2012/197375; 2012/0203316; 2012/0203320; 2012/0203321; 2013/0197424; 2013/0197602; 2014/0039587; 2014/0353001; 2014/0358208; 2014/0358209; 2014/0358210; 2015/0045864; 2015/0066120; 2015/0018915; and 2015/0051681, all of which are incorporated herein by reference.

One or more percutaneous leads, such as lead 12 in FIG. 1 or lead 112 in FIG. 2 , can be implanted for stimulation. In at least some embodiments, multiple percutaneous leads can be implanted and spaced apart from each other. Such an arrangement can be useful for, for example, spinal cord stimulation to stimulation two regions of the spinal cord or for deep brain stimulation to stimulated opposite hemispheres of the brain. For example, one or more percutaneous leads can be implanted on each lateral side of the spinal cord and arranged over or near the dorsal columns or dorsal horns. Optionally, a medial percutaneous lead may also be implanted.

FIG. 4 illustrates one embodiment of three percutaneous leads 412 a, 412 b, 412 c with multiple electrodes 426 (which may be ring electrodes, tip electrodes, segmented electrodes, or any combination thereof) disposed along the lead body 410 of each percutaneous lead. Each lead 412 a, 412 b, 412 c can include any number of electrodes 426 including, but not limited to, one, two, three, four, five, six, seven, eight, nine, ten, twelve, sixteen, or more electrodes.

Paddle leads can be an alternative to percutaneous leads. FIG. 5 illustrates one embodiment of a paddle lead 512 with a paddle body 511, multiple columns of electrodes 526, and one or more lead bodies 510 extending from the paddle body 522. Each of the columns can include any number of electrodes 526 including, but not limited to, one, two, three, four, five, six, seven, eight, nine, ten, twelve, sixteen, or more electrodes. The electrodes 534 in each of the columns can be spaced apart longitudinally in a uniform manner, as illustrated in FIG. 5 , or in any other regular or irregular pattern. The columns may have the same number of electrodes 526 or different numbers of electrodes. The columns can be identical with respect to arrangement of the electrodes 526 or can be different.

FIG. 3 is a schematic overview of one embodiment of components of an electrical stimulation system 300 including an electronic subassembly 310 disposed within an IPG 14 (FIG. 1 ). It will be understood that the electrical stimulation system can include more, fewer, or different components and can have a variety of different configurations including those configurations disclosed in the stimulator references cited herein.

The IPG 14 (FIG. 1 ) can include, for example, a power source 312, antenna 318, receiver 302, processor 304, and memory 303. Some of the components (for example, power source 312, antenna 318, receiver 302, processor 304, and memory 303) of the electrical stimulation system can be positioned on one or more circuit boards or similar carriers within a sealed housing of the IPG 14 (FIG. 1 ), if desired. Unless indicated otherwise, the term “processor” refers to both embodiments with a single processor and embodiments with multiple processors.

An external device, such as a CP or RC 306, can include a processor 307, memory 308, an antenna 317, and a user interface 319. The user interface 319 can include, but is not limited to, a display screen on which a digital user interface can be displayed and any suitable user input device, such as a keyboard, touchscreen, mouse, track ball, or the like or any combination thereof.

Any power source 312 can be used including, for example, a battery such as a primary cell battery or a rechargeable battery. Examples of other power sources include super capacitors, nuclear or atomic batteries, mechanical resonators, infrared collectors, thermally-powered energy sources, flexural powered energy sources, bioenergy power sources, fuel cells, bioelectric cells, osmotic pressure pumps, and the like including the power sources described in U.S. Pat. No. 7,437,193, incorporated herein by reference in its entirety.

If the power source 312 is rechargeable battery, the battery may be recharged using the antenna 318, if desired. Power can be provided to the battery for recharging by inductively coupling the battery through the antenna to an optional recharging unit 316 external to the user. Examples of such arrangements can be found in the references identified above.

In one embodiment, electrical current is emitted by the electrodes 26 on the lead body to stimulate nerve fibers, muscle fibers, or other body tissues near the electrical stimulation system. A processor 304 is generally included to control the timing and electrical characteristics of the electrical stimulation system. For example, the processor 304 can, if desired, control one or more of the timing, frequency, amplitude, width, and waveform of the pulses. In addition, the processor 304 can select which electrodes can be used to provide stimulation, if desired. In some embodiments, the processor 304 may select which electrode(s) are cathodes and which electrode(s) are anodes. In some embodiments, the processor 304 may be used to identify which electrodes provide the most useful stimulation of the desired tissue. Instructions for the processor 304 can be stored on the memory 303. Instructions for the processor 307 can be stored on the memory 308.

Any processor 304 can be used for the IPG and can be as simple as an electronic device that, for example, produces pulses at a regular interval or the processor can be capable of receiving and interpreting instructions from the CP/RC 306 (such as CP 18 or RC 16 of FIG. 1 ) that, for example, allows modification of pulse characteristics. In the illustrated embodiment, the processor 304 is coupled to a receiver 302 which, in turn, is coupled to the antenna 318. This allows the processor 304 to receive instructions from an external source to, for example, direct the pulse characteristics and the selection of electrodes, if desired. Any suitable processor 307 can be used for the CP/RC 306.

Any suitable memory 303, 308 can be used including computer-readable storage media may include, but is not limited to, volatile, nonvolatile, non-transitory, removable, and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer-readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory, or other memory technology, CD-ROM, digital versatile disks (“DVD”) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a processor.

In one embodiment, the antenna 318 is capable of receiving signals (e.g., RF signals) from an antenna 317 of a CP/RC 306 (see, CP 18 or RC 16 of FIG. 1 ) which is programmed or otherwise operated by a user. The signals sent to the processor 304 via the antenna 318 and receiver 302 can be used to modify or otherwise direct the operation of the electrical stimulation system. For example, the signals may be used to modify the pulses of the electrical stimulation system such as modifying one or more of pulse width, pulse frequency, pulse waveform, and pulse amplitude. The signals may also direct the electrical stimulation system 300 to cease operation, to start operation, to start signal acquisition, or to stop signal acquisition. In other embodiments, the stimulation system does not include an antenna 318 or receiver 302 and the processor 304 operates as programmed.

Optionally, the electrical stimulation system 300 may include a transmitter (not shown) coupled to the processor 304 and the antenna 318 for transmitting signals back to the CP/RC 306 or another unit capable of receiving the signals. For example, the electrical stimulation system 300 may transmit signals indicating whether the electrical stimulation system 300 is operating properly or not or the level of charge remaining in the battery. The processor 304 may also be capable of transmitting information about the pulse characteristics so that a user or clinician can determine or verify the characteristics.

Transmission of signals can occur using any suitable method, technique, or platform including, but not limited to, inductive transmission, radiofrequency transmission, Bluetooth™, Wi-Fi, cellular transmission, near field transmission, infrared transmission, or the like or any combination thereof. In addition, the IPG 14 can be wirelessly coupled to the RC 16 or CP 18 using any suitable arrangement include direct transmission or transmission through a network, such as a local area network, wide area network, the Internet, or the like or any combination thereof. The CP 18 or RC 16 may also be capable of coupling to, and sending data or other information to, a network 320, such as a local area network, wide area network, the Internet, or the like or any combination thereof.

The methods and systems described herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Accordingly, the methods and systems described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Systems referenced herein typically include memory and typically include methods for communication with other devices including mobile devices. Methods of communication can include both wired and wireless (for example, RF, optical, or infrared) communications methods and such methods provide another type of computer readable media; namely communication media. Wired communication can include communication over a twisted pair, coaxial cable, fiber optics, wave guides, or the like, or any combination thereof. Wireless communication can include RF, infrared, acoustic, near field communication, Bluetooth™, or the like, or any combination thereof.

In at least some embodiments, the selection of one or more electrodes for stimulation, as well as the selection of the stimulation amplitude for each electrode, determines a stimulation position along the lead. In at least some embodiments, the stimulation position corresponds to a virtual electrode from which the electrical stimulation appears to arise for the particular electrode selection and stimulation amplitude(s). In at least some embodiments, the stimulation position can correspond to a composite of the selected electrode(s).

When an electrical stimulation system is programmed, the programmer (for example, a clinician, patient, or other individual) selects stimulation parameters, including the selection of electrode(s) and corresponding amplitude(s), that provide a stimulation benefit. In at least some embodiments, different sets of stimulation parameters are tested to determine which set of stimulation parameters provides a desired stimulation benefit (which may also include the absence, or lower severity, of side effects.) This set of programmed stimulation parameters can be thought of as providing stimulation from a primary stimulation position along the lead.

In at least some instances, it is found that the effectiveness of the primary stimulation position may change over time due to stimulation drift. In at least some embodiments, it may be desirable to monitor stimulation drift. In at least some embodiments, it may be desirable to alter the stimulation parameters to change the primary stimulation position along the lead.

Stimulation drift may occur for a variety of reasons or any combination thereof. For example, in at least some instances, an electrical stimulation lead may migrate over time. For example, a spinal cord stimulation lead may move over time due to, for example, patient movement. With migration, the primary stimulation position programmed for the lead may no longer be as desirable for stimulating the patient and it may be beneficial to alter the stimulation parameters to change the primary stimulation position.

In at least some instances, the target of stimulation may move over time or the stimulated tissue may change physiologically or become desensitized. For example, in spinal cord stimulation for pain, the site(s) of the pain may change over time and so the corresponding target of stimulation to relieve the pain may be different. In at least some embodiments, it can be beneficial to alter the stimulation position in view of the change in the target of stimulation or the changing/desensitizing of the stimulated tissue.

The systems and methods described herein can address these issues or any other cause(s) of stimulation drift that occur over time. The systems and methods incorporate modulation of the stimulation position. In at least some embodiments, the methods and systems described herein can monitor stimulation performance and effectiveness statistically by modulation of the stimulation position. In at least some embodiments, the systems and methods can detect stimulation drift over time, which may occur for a one or more reasons (or for an unknown reason) including, but not limited to, lead migration, changes in the site of the stimulation target, or changes/desensitization of the stimulated tissue.

FIG. 6 is a flowchart of one embodiment of a method for monitoring or addressing stimulation drift. In step 602, electrical stimulation is directed through the electrodes of at least one lead. The electrical stimulation can be thought of as arising from a stimulation position that is based on the selection of one or more electrodes of the lead(s) and the stimulation amplitude for each electrode. When the electrical stimulation system is programmed, there is a selection of the electrode(s) and stimulation amplitude(s) which correspond to an initial primary stimulation position. As described below, the primary stimulation position can be altered by altering the selection of electrode(s) and stimulation amplitude(s). In at least some embodiments, such alteration can be performed manually by a programmer, clinician, user, or other individual. In at least some embodiments, such alteration can be performed automatically by the electrical stimulation system. In at least some embodiments, both manual and automatic alterations are available.

In step 604, the stimulation position is modulated over time around the primary stimulation position. In at least some embodiments, the modulation occurs by altering at least one of i) the selection of electrode(s) or ii) the stimulation amplitude for at least one selected electrode. By modulating the stimulation position, different stimulation positions can be tested. In at least some embodiments, such modulation and testing can be used to monitor stimulation drift. In at least some embodiments, such modulation and testing can be used for other purposes.

FIG. 7 is a graphical illustration of stimulation position with a center stimulation position in the center 770 and the concentric circles 772, 774, 776 representing physical distance away from the center stimulation position. In at least some embodiments, the primary stimulation position is positioned at the center 770. In other embodiments, the primary stimulation position may be anywhere on the graphical illustration. In FIG. 7 , the track 778 shows modulation of the stimulation position over time.

Any suitable number of different stimulation positions can be tested during any particular modulation period including, but not limited to, one, two, three, four, six, eight, ten, twelve, twenty, or more stimulation positions. The number of stimulation positions that are tested may be dependent on the duration of the modulation.

In at least some embodiments, the modulation of the stimulation position tests stimulation positions in at least two, three, or four quadrants 771, 773, 775, 777 positioned around the primary stimulation position at the center 770. In at least some embodiments, the quadrants are defined by a line 779 a that extends along a longitudinal axis of the lead and a line 779 b that is orthogonal to the longitudinal axis of the lead. Other definitions of the quadrants can be used and lines other than those defined by the longitudinal axes can be used. It will also be recognized that the site of the primary stimulation position (for example, at or near the distal-most or proximal-most electrode) may preclude modulating the stimulation position in one or more directions. In at least some embodiments, if the stimulation positions are in only two of the quadrants, then those quadrants are opposite each other with respect to the center 770 (for example, quadrants 771, 775 or quadrants 773, 777.)

In at least some embodiments, the modulation of the stimulation position can be performed continuously. In at least some embodiments, the modulation of the stimulation position can be turned on or off by a user control (for example, a user control on the RC 16 or CP 18 in FIG. 1 ) or by system control.

In at least some embodiments, the modulation of the stimulation position can be performed periodically with stimulation at the primary stimulation position occurring except for modulation periods when the stimulation position is modulated. The length of the modulation period can be any suitable amount of time such as, for example, but not limited to, at least 1, 2, 5, 10, 15, 20, 30, 45, 90, or 150 minutes or 1, 2, 3, 4, 5, 6, 12, or 18 hours or 1, 2, 5, or more days or 1, 2, 4, 6, or 8 weeks. In at least some embodiments, the length of each of the modulation periods is the same. In at least some embodiments, the length of a modulation period may differ from the length of another modulation period. In at least some embodiments, the lengths of the different modulation periods may be manually selected, automatically selected by the electrical stimulation system, or may be randomly or pseudo-randomly selected.

The time interval (e.g., a non-modulation interval) between modulation periods can be any suitable amount of time such as, for example, but not limited to, at least 1, 2, 5, 10, 15, 20, 30, 45, 90, or 150 minutes or 1, 2, 3, 4, 5, 6, 12, or 18 hours or 1, 2, 5, 10, 12, or 30 days or 1, 2, 4, 6, or 8 weeks, or 1, 2, 3, 4, 6, or more months. In at least some embodiments, the time interval between modulation periods is the same. In at least some embodiments, the time interval between modulation periods may differ. In at least some embodiments, the time intervals between modulation periods may be manually selected, automatically selected by the electrical stimulation system, or may be randomly or pseudo-randomly selected.

In step 606, a measure of stimulation effect at the modulated stimulation positions is received or observed.

In at least some embodiments, the measure of stimulation effect can be determined using one or more sensors (such as sensors 40 in FIG. 1 .) In at least some embodiments, the sensor(s) can be part of the electrical stimulation system or part of the implantable pulse generator/stimulation lead. For example, the implantable pulse generator can be capable of monitoring electrical signals from the tissue near the lead using the electrodes of the lead. Examples of such signals can include, but are not limited to, evoked composite action potentials (ECAP), evoked resonant neural activities (ERNA), electrospinograms (ESG), electroencephalograms (EEG), heart rate, respiratory rate, or the like or any combination thereof.

In at least some embodiments, the sensor(s) can be external of the implantable pulse generator or the electrical stimulation system. For example, a sensor to measure pain, tremor, or other symptoms associated with the disease or disorder being treated by electrical stimulation can be used. A sensor can communicate with the implantable pulse generator or the electrical stimulation system to provide sensor signals that can then be interpreted or used as the measure of stimulation effect.

In at least some embodiments, the measure of stimulation effect can be a patient response. For example, the patient may provide a response to a query regarding pain, tremor, or another symptom associated with the disease or disorder being treated by electrical stimulation. Such a response may be provided through the RC 16, CP 18, or any other suitable device (for example, a mobile phone or tablet that is in communication with the electrical stimulation system.) Another example is monitoring the patient changing the amplitude of the stimulation using, for example, the RC 16 or any other suitable device (for example, a mobile phone or tablet that is in communication with the electrical stimulation system.) Increasing the amplitude may be indicative that stimulation at the current stimulation position is less effective and, therefore, requires more energy to provide a suitable benefit for the patient. Decreasing the amplitude may be indicative of stimulation at the current stimulation position causing side effects.

In at least some embodiments, a patient response to the modulation of the stimulation position is used to determine whether the current stimulation position (arising from the modulation) results in noticeably different stimulation from the primary stimulation position. FIG. 8 illustrates one embodiment of a method for monitoring whether the modulation of the stimulation position produces noticeably different stimulation. In at least some embodiments, the steps in FIG. 8 may be part of step 604 of FIG. 6 or part of the combination of steps 604 and 606 of FIG. 6 .

In step 802, the stimulation position is modulated (e.g., altered) and the patient is stimulated. In step 804, the implantable pulse generator or the electrical stimulation system (such as the RC or CP) monitors whether the patient alters the stimulation intensity (e.g., the total stimulation amplitude, which is related to, but not necessarily the same as, the amplitude at the individual electrode(s)) in response to the modulation of the stimulation position.) In at least some embodiments, the patient can alter the stimulation intensity using one or more controls on the RC 16 or other device. If no alteration is performed, then in step 806, the change in the stimulation position (e.g., the modulation) is increased. If yes, then, at least in some embodiments, the altered stimulation amplitude can be used as a measure of the stimulation effect.

In at least some embodiments, when the stimulation position is modulated, the stimulation amplitude at one or more of the selected electrodes may be lower or reduced to increase the likelihood that the patient will alter the stimulation intensity. The stimulation intensity selected by the patient can be representative of the effectiveness of stimulation at that stimulation position. In at least some embodiments, higher stimulation intensity may be indicative of lower effectiveness and lower stimulation intensity may be indicative of higher effectiveness or may be indicative of the presence or an increase in side effects.

Returning to FIG. 6 , in steps 608 and 610, the measures of stimulation effect are monitored to determine when there is stimulation drift. In at least some embodiments, stimulation drift can be indicated by changes in the measures that are indicative of the effectiveness of stimulation at the primary stimulation position or at other stimulation positions.

In at least some embodiments, the monitoring can utilize statistical analysis to determine when the measures indicate stimulation drift. Demodulation of the monitoring data may isolate noise from correlations between the stimulation position and the measure of stimulation effect. In at least some embodiments, any suitable filtering or adaptive filtering technique can be used. In at least some embodiments, the measures of stimulation effect are demodulated based on the modulation of the stimulation position.

In at least some embodiments, the determination of stimulation drift is based on one or more drift criteria. Examples of such drift criteria can include, but are not limited to, a stimulation position at which the patient applies a stimulation amplitude that is lower by a threshold amount than the stimulation amplitude applied by the patient at the primary stimulation position; an increase, by a threshold amount, of the stimulation amplitude applied by the patient at the primary stimulation position; or the like or any combination thereof.

When no stimulation drift is indicated according to at least one drift criterion, the method returns to step 602. If stimulation drift is indicated according to at least one drift criterion, then in step 612, the primary stimulation position is altered or a message is generated (or both the primary stimulation position is altered or the message is generated.)

As an example, with the primary stimulation position at (x, y), the stimulation position can be modulated to a position (x+delta, y) and a measure of stimulation effect can be received over a week or any other suitable period. The stimulation position can then be modulated to a position (x−delta, y) and a measure of stimulation effect can be received over a week or any other suitable period. The system can repeat this modulation several times and average the results. The system can alter the primary stimulation position to an x position in the range of x+delta and x−delta based on the monitoring.

In at least some embodiments, the primary stimulation position can be altered from the current primary stimulation position to a new primary stimulation position by altering at least one of i) the selection of electrode(s) or ii) the stimulation amplitude for at least one of the selected electrode(s) or iii) any combination of i) and ii). In at least some embodiments, the methods and systems described herein provide closed loop adjustment of the stimulation parameters to address stimulation drift by altering the primary stimulation position as stimulation drift is identified. In at least some embodiments, the methods and systems generate a message (for example, an alert or a warning) to the patient, a clinician, or any other suitable individual (or any combination of these people) when the primary stimulation position is, or will be, altered. In at least some embodiments, the patient, clinician, or any other suitable individual may be given the option to cancel the alteration. In at least some embodiments, the patient, clinician, or any other suitable individual may be asked to confirm the alteration.

In at least some embodiments, the method and systems described herein generate a message (for example, an alert or a warning) when stimulation drift occurs. In at least some embodiments, the methods and system described herein generate a message (for example, an alert or a warning) when a determination is made that the stimulation lead is no longer in a desirable position (for example, if the stimulation lead has migrated) or should be moved or explanted.

It will be understood that each block of the flowcharts, and combinations of blocks in the flowcharts and methods disclosed herein, can be implemented by computer program instructions. These program instructions may be provided to a processor to produce a machine, such that the instructions, which execute on the processor, create means for implementing the actions specified in the flowchart block or blocks disclosed herein. The computer program instructions may be executed by a processor to cause a series of operational steps to be performed by the processor to produce a computer implemented process. The computer program instructions may also cause at least some of the operational steps to be performed in parallel. Moreover, some of the steps may also be performed across more than one processor, such as might arise in a multi-processor computing device. In addition, one or more processes may also be performed concurrently with other processes, or even in a different sequence than illustrated without departing from the scope or spirit of the invention.

The computer program instructions can be stored on any suitable computer-readable medium including, but not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (“DVD”) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computing device.

The above specification provides a description of the manufacture and use of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended. 

What is claimed as new and desired to be protected by Letters Patent of the United States is:
 1. An electrical stimulation system, comprising: a lead comprising a plurality of electrodes disposed along a distal portion of the lead; and an implantable control module coupled, or coupleable, to the lead and configured for implantation in a patient, the implantable control module comprising a processor configured for performing actions, comprising directing electrical stimulation through the electrodes of the lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of the implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position by altering at least one of i) the selection of the one or more electrodes or ii) the stimulation amplitude for at least one of the one or more selected electrodes and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.
 2. The electrical stimulation system of claim 1, wherein the modulating comprises modulating the stimulation position during a plurality of modulation periods, wherein the modulation periods are separated by non-modulation intervals.
 3. The electrical stimulation system of claim 2, wherein the modulation period has a duration of at least 30 minutes and the non-modulation interval has a period of at least 30 minutes.
 4. The electrical stimulation system of claim 1, wherein the modulating comprises modulating the stimulation position continuously over the time period.
 5. The electrical stimulation system of claim 1, wherein the modulating comprises modulating the stimulation position to provide stimulation positions during the modulation in at least three different quadrants around the primary stimulation position.
 6. The electrical stimulation system of claim 1, wherein altering the primary stimulation position comprises altering the stimulation position only after confirmation from a user.
 7. The electrical stimulation system of claim 1, wherein the modulating comprises modulating the stimulation position; assessing whether a patient increases a stimulation intensity in response to the modulation; and when the assessment is negative, increasing a change in the stimulation position from the primary stimulation position.
 8. The electrical stimulation system of claim 1, wherein the performing comprises performing the altering of the primary stimulation position, the actions comprising an automated closed loop adjustment of the primary stimulation position in response to stimulation drift.
 9. A method for monitoring stimulation drift, the method comprising: directing electrical stimulation through the electrodes of the lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of the implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position by altering at least one of i) the selection of the one or more electrodes or ii) the stimulation amplitude for at least one of the one or more selected electrodes and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.
 10. The method of claim 9, wherein the modulating comprises modulating the stimulation position during a plurality of modulation periods, wherein the modulation periods are separated by non-modulation intervals.
 11. The method of claim 9, wherein the modulating comprises modulating the stimulation position continuously over the time period.
 12. The method of claim 9, wherein the modulating comprises modulating the stimulation position to provide stimulation positions during the modulation in at least three different quadrants around the primary stimulation position.
 13. The method of claim 9, wherein altering the primary stimulation position comprises altering the stimulation position only after confirmation from a user.
 14. The method of claim 9, wherein the modulating comprises modulating the stimulation position; assessing whether a patient increases a stimulation intensity in response to the modulation; and when the assessment is negative, increasing a change in the stimulation position from the primary stimulation position.
 15. A non-transitory computer-readable medium having processor-executable instructions for monitoring stimulation drift, the processor-executable instructions when installed onto a device enable the device to perform actions, the actions comprising: directing electrical stimulation through the electrodes of the lead, wherein a selection of one or more electrodes and a stimulation amplitude for each of the one or more selected electrodes determines a stimulation position, wherein user programming of the implantable control module initially selects a primary stimulation position; modulating, over a time period of at least one day, the stimulation position around the primary stimulation position by altering at least one of i) the selection of the one or more electrodes or ii) the stimulation amplitude for at least one of the one or more selected electrodes and delivering electrical stimulation at the modulated stimulation positions; for at least a plurality of the modulated stimulation positions and the primary stimulation position, receiving or observing a measure of stimulation effect; monitoring the measures of stimulation effect; and when the monitoring indicates a stimulation drift based on at least one drift criterion, performing at least one of the following: i) altering the primary stimulation position, or ii) generating a message.
 16. The non-transitory computer-readable medium of claim 15, wherein the modulating comprises modulating the stimulation position during a plurality of modulation periods, wherein the modulation periods are separated by non-modulation intervals.
 17. The non-transitory computer-readable medium of claim 15, wherein the modulating comprises modulating the stimulation position continuously over the time period.
 18. The non-transitory computer-readable medium of claim 15, wherein the modulating comprises modulating the stimulation position to provide stimulation positions during the modulation in at least three different quadrants around the primary stimulation position.
 19. The non-transitory computer-readable medium of claim 15, wherein altering the primary stimulation position comprises altering the stimulation position only after confirmation from a user.
 20. The non-transitory computer-readable medium of claim 15, wherein the modulating comprises modulating the stimulation position; assessing whether a patient increases a stimulation intensity in response to the modulation; and when the assessment is negative, increasing a change in the stimulation position from the primary stimulation position. 